The present experiment addresses whether conjunctive stimulus presentations are important for morphological plasticity of Purkinje cells in the cerebellar cortex. Purkinje cell morphology was compared in naive rabbits and in rabbits that underwent paired and unpaired eyeblink conditioning to test whether neuronal morphological plasticity is restricted to conditions in which stimulus presentations are temporally contiguous. To direct the conditioned stimulus (CS) information to the cerebellar cortex, pontine stimulation served as the CS and airpuffs were used for the unconditioned stimulus (US). The paired rabbits received pontine stimulation for 350 msec paired with a co-terminating airpuff (100 msec). Unpaired rabbits received the same stimuli, but presented in a random order with 1-32 seconds delay between them. Rabbits in the trained groups received an average of 12 days of training. Golgi-stained Purkinje neurons in lobule HVI were analyzed for main and spiny dendritic branch length and numbers. All statistically significant differences seen were between the naive groups and the paired and unpaired groups. Total dendritic length, main branch length, and total spiny branch length were all greater in the naive group than in the paired and unpaired groups which did not differ. Spiny branch arbors were larger, but fewer in number, in the paired and unpaired groups than in the naive group. No differences were found between the paired and unpaired conditions, or between the hemispheres ipsilateral and contralateral to the trained eye. In summary, the Purkinje cell morphological changes detected with these methods appear to be activation-induced, and not uniquely related to the conjunctive activation of the CS and US in the paired condition which is required for the conditioned eyeblink response. Temporally contiguous stimuli do not appear to be necessary for the induction of structural changes in Purkinje cell dendritic arbors, nor do temporal associations appear to facilitate structural changes of Purkinje cell dendritic arbors. Both main branches and spiny branches in the paired and unpaired groups differed from the naive group. Hence, plasticity is not restricted to Purkinje cell spiny branches.